1. Field of the Invention
The present invention relates to apparatus for determining by weight the actual or proportional amount of a volatile fluid in a test sample and, more particularly, to apparatus for evaporating, collecting and weighing a volatile fluid of interest contained in the sample under test.
2. Description of Related Art
Various devices have been developed for determining the quantity, usually by weight, of a volatile fluid present within a test sample. Such determinations are important for quality control in manufacturing and, in some cases, required by law. One technique, known as loss on drying, for determining and measuring the amount of volatile fluid within a sample under test is described in U.S. Pat. No. 4,165,633. Therein is described apparatus for heating a test sample at a temperature of interest in view of the volatile fluid(s) to be measured. The change in weight of the sample prior to, during and subsequent to evaporation of the volatile fluid(s) of interest provides data for computing the percent by weight of the volatile fluid of interest in the test sample. Various computational techniques are employed to forecast the percentage determination based upon the initial weight loss rate. Such computational approximations reduce the time required to complete a test without serious derogation of the accuracy of the determination. Generally, loss on drying techniques are limited to approximately 0.1% minimum moisture loss due to secondary effects such as convective air currents, buoyancy effects and temperature gradients.
Various other sensors are presently in use to measure the quantity of volatile fluid in a gas stream. Of these types, infrared and capacitive sensors are capable of providing instantaneous measurements of the concentration of volatile fluid of interest in a gas stream passing through the sensor. To determine the amount of volatile fluid by weight, the readings provided by these sensors would have to be integrated over the time period of the test in order to obtain an approximation of sufficient accuracy to be useful in a variety of circumstances and to satisfy the differing criteria of various industries. Other problems such as preexisting moisture levels, transient response times and contamination which may be present in these types of sensors must be addressed. Another process is known as Karl Fischer analysis, uses toxic and cumbersome wet chemistry and amperommetry.